As is well known in the art, hot runner injection molding systems have a manifold to convey the pressurized melt from the inlet at a molding machine to one or more outlets, each of which lead to a nozzle which, in turn, extends to a gate to an injection mold cavity. Manifolds and nozzles have various configurations, depending upon the number and arrangement of the cavities. It is known to be desirable to provide a means of heating the manifold and/or nozzles to maintain a desired temperature distribution across the manifold and/or nozzle. Various means of heating manifolds and nozzles are known. For instance, a manifold can have an electrical heating element integrally cast or brazed into the manifold, as described respectively in U.S. Pat. Nos. 4,688,622 to Gellert and 4,648,546 to Gellert, a cartridge heater can be cast in the manifold, as disclosed in U.S. Pat. No. 4,439,915 to Gellert, or a plate heater can be positioned adjacent the manifold to provide heat thereto, as disclosed in pending U.S. application Ser. No. 09/327,490, filed Jun. 8, 1999 now U.S. Pat. No. 6,447,283 and concurrently owned herewith. Similarly, a nozzle may have an integral heater element brazed therein, as shown in U.S. Pat. No. 4,557,685 to Gellert, may have a heated sleeve disposed around the nozzle, as shown in U.S. Pat. Nos. 5,411,392 and 5,360,333 to Von Buren and Schmidt, respectively, or may employ a film heater as shown in U.S. Pat. No. 5,973,296.
The high pressures and temperatures and numerous cycles experienced in injection molding systems requires manifold, nozzle and heater components to be fabricated of high strength materials, typically high strength tools steels, such as H13. Such materials also typically have good corrosion resistance properties, which is beneficial as is well known in the art. Tools steels, however, have poor thermal conductivity, making exacting control over runner and gate temperatures difficult. Materials such as copper, however, though highly thermally conductive, typically have low strength and hardness in comparison to tool steels. Further, copper and its alloys also have a very poor corrosion resistance. Though, other thermally conductive materials are known, such as refractory alloys like molybdenum and tungsten, these materials can be prohibitively expensive, not to mention difficult to machine.
For some applications, it is known that high strength and high thermal conductivity can be achieved through the use of so-called ‘metal infiltration’ techniques, wherein a porous skeleton composed of a high strength metal is infiltrated by a thermally conductive metal to yield a two-phase composite part having improved characteristics over both component metals. U.S. Pat. No. 4,710,223 to Matejcezyk discloses an infiltration method for achieving super erosion and high-temperature resistance in rocket nozzles and reaction engines by infiltrating a refractory metal, such as molybdenum or tungsten, with copper or an alloy of copper. U.S. Pat. No. 5,775,402 to Sachs discloses a process of so-called ‘three dimensional printing’ whereby a metal powder/binder mixture is deposited in layers by computer-controlled machinery to fabricate the complexly-shaped preform layer-by-layer. The preform is then sintered and infiltrated according to known techniques to achieve a two-phase material having good strength and temperature conductivity. Sachs however, requires complex programming and machinery to achieve the preform.
There is a need for achieving injection molding manifold, nozzle and heater components with increased thermal conductivity without sacrificing strength and, further, there is a need for achieving such parts through simpler fabrication techniques.
As noted above, injection molding components can be heated by an integral heater, such as disclosed in U.S. Pat. No. 4,648,546 to Gellert. Typically, a brazing or bonding step is required to join the heater element to the component, to obtain good heat transfer characteristics between the element and the manifold, nozzle and/or heater. This brazing step, however, requires additional effort and time in the tooling process.
Accordingly, there is also a need for a reduction in the number of manufacturing and tooling operations required in making high strength and highly thermally conductive manifolds, nozzles and heaters.